7. PROJECT SUMMARY ABSTRACT Although the majority of AD patients are sporadic, several factors that increase risk or susceptibility to developing AD-related pathology and cognitive decline have been identified. Specifically, traumatic brain injury (TBI) has been linked to an increased susceptibility to AD and AD-related dementia many years after the initial injury. Amyloid-dependent and -independent mechanisms have been postulated to explain the risk inducing effect of TBI, but the molecular and cellular mechanisms by which TBI increases AD disease risk remain unclear. Current studies to examine the link between the mechanical injury associated with TBI and development of AD-related phenotypes have been limited to (i) rodent models, which while have provided valuable information in understanding possible connections between TBI and AD, do not recapitulate all aspects of the human disease and (ii) neuronal cells from cadaveric tissue samples which only provide an end- stage view of the disease and rapidly loose disease-related phenotypes upon extensive ex vivo culture. With hiPSC technology, it is possible to obtain a fully differentiated cell type (such as a skin cell) from an AD patient and reprogram it back into a cell type that is capable of differentiating into all of the cell types of the mature, adult body (such as neural cells of the cortex). Although we and others have used AD hiPSC-derived neural cells to study this disease in a simplified and accessible system, applying hiPSC-based technologies to study the connection between TBI-related cellular injuries and the onset of AD-related phenotypes has not yet been achieved. To that end, we will use our collective experience in stem cell bioengineering and neurodegenerative disease modeling to develop a highly accessible in vitro model to elucidate potential genetic, molecular, and cellular mechanisms by TBI-induced cellular injuries lead to AD onset and age-related progression. In the first aim of this proposal, we will validate an electro-mechanical cell-shearing model of TBI using 3-D hiPSC derived neuronal-astrocytic co-cultures. In the second aim, subsequent phenotypic analysis of injured and uninjured 3- D cortical cultures derived from non-demented control and AD hiPSCs will reveal the (i) direct effect of the mechanical injury on susceptibility to AD-related toxic stimuli, (ii) potential signaling pathways and transcriptional targets that are independently influenced by mechanical injury and disease status and (iii) effect of mechanical insults on the manifestation or augmentation of AD-related phenotypes. Overall, the ability to identify definitive relationships between mechanical injury and AD-related phenotypes will have a significant translational impact on the design of molecularly targeted therapies to treat the many patients suffering from TBI-induced AD.